The use and provision of daylight (daylighting) is becoming of increasing concern to architects and building engineers. Daylight can enhance the appearance of interior spaces, and can provide building occupants with social and psychological benefits. In addition, daylight can be used as a substitute or supplement to artificial lighting, which may reduce the overall energy usage of a building and impart substantial savings to building owners/occupants.
Traditionally, windows have been used as the primary mechanism for admitting daylight to the interior of a building. While windows can admit a great deal of light into an interior space, their usefulness for daylighting is limited by several factors. For example, windows can cause substantial solar heating of building interior spaces, particularly when used in large numbers. This can cause discomfort to building occupants, and may increase the load on air conditioning systems used to control the temperature of interior spaces in the building. Further, windows may not enable natural light to penetrate to all interior spaces of a building, particularly those interior spaces that are remote from the exterior walls of the building. Due to the limited applicability of windows, solar tubes (also known light tubes, light pipes, or daylight pipes) are used in many applications. Solar tubes are structures that transport and/or distribute natural light (and optionally artificial light) from one location (e.g., but not limited to, a rooftop) to another location (e.g., but not limited to, an interior location within a structure/building) for the purpose of illumination.
Recently, artificial light sources have been combined with daylight systems. For example, some known daylight harvesting systems 1, FIG. 1A, include a natural light provider 2 (e.g., a window and/or solar tube) for providing natural light 3 in the space/environment 4 from the sun 5, an artificial light source 6 for providing artificial light 7, a luminosity (lux) sensor 8 that measures the luminosity (e.g., brightness) of the light (e.g., the total light and/or the natural light 3) in the space/environment 4, and a controller 9 that adjusts the brightness of the artificial light source 6 in response to the lux sensor 8. As a result, the energy consumption of the artificial light source 6 may be reduced when there is sufficient natural light 3 in the space/environment 4. While these daylight harvesting systems 1 are generally inexpensive and can save energy, they are limited to adjusting the brightness of the artificial light source 6 and cannot adjust the CCT of the artificial light 7 based on changes to the natural lighting 3. As a result, they cannot be used in many applications that require the ability to adjust the CCT of the artificial light 7 based on the conditions of the natural light 3.
The only daylight systems 10 known to the inventors that can adjust the brightness and the CCT of the artificial light source based on the natural lighting are generally illustrated in FIG. 1B. These daylight systems 10 include a natural light provider 2 (e.g., a window and/or solar tube) for providing natural light 3 in the space/environment 4 from the sun 5, a color-tunable light source 11 for providing artificial light 7, a luminosity (lux) sensor 8 that measures the luminosity (e.g., brightness) of the light (e.g., the total light and/or the natural light 3) in the space/environment 4, a CCT sensor 12 that measures the CCT of the natural light 3, and a controller 13 that adjusts the brightness of the artificial light source 6 in response to the lux sensor 8 and adjusts the CCT of the artificial light 7 based on the measured CCT output signal from the CCT sensor 12 to achieve the desired overall lighting conditions in the space/environment 4. While these known daylight systems 10 are generally effective, the need for both a CCT sensor 12 and a lux sensor 8 increases the overall cost and complexity of the daylight system 10.
Accordingly, what is needed is a daylight system and method that can adjust the CCT of an artificial light source (e.g., color-tunable light source) without the need of a CCT sensor. For example, a daylight system and method is needed that can adjust the CCT of an artificial light source based on the luminosity of the only the natural light without the use or need of a CCT sensor. Additionally, a daylight system and method is needed that can adjust the CCT and the brightness of an artificial light source based on the luminosity of the natural light and the total luminosity of the light in the environment without the use or need of a CCT sensor.